300/440/550 300SX Compression???

[TreeMoney]

I've got a 300sx that I'm building for my buddy's son for x-mas and I'm having an issue getting it started.

First off, it's got 180lb of compression... I can't believe this is stock. Does anyone know what it was originally?

The problem is, when I am trying to start the ski, the sprag clutch is slipping and making a terrible noise. So I'm thinking the compression is too high and the sprag trying to grab the starting gear hub is the weak link.

I've inspected the sprag clutch and the ID of the race and everything looks OK.

Does anyone have any ideas???

 

[N2 H2O]

Stock compression is 150. Are you sure the battery is good? One of my skis did that when the battery got weak. Take off the flywheel cover and see if the flywheel teeth are damaged. The bendix on the starter could also be going bad.

 

[Austin]

Had the same problem.. I thought my battery kept going dead but went bought new battery still did the same thing. It ended up being my starter was going bad. Not saying is not your battery but put a volt meter on your battery and see if its around 11 or 12 volts, if it is then its probably your starter.

Sounds like the head might have been milled or the cylinders have been decked.

 

[N2 H2O]

If the battery is 11 or 12 volts, test your power at the starter to make sure there's not an electrical problem.

 

[TreeMoney]

Thanks guys...

I am confident the battery is good. It turns over my FZR (1.8L SC Yamaha). The starter looks fine, it's not bloated or rusty at all and without a plug in it, the starter is able to turn the motor over fine, no matter how many times or how long i keep it turning over.

I bought another head, the head that was on it, was clearly milled. So much so that the tab on the side of the head is even cut. I was getting compression readings of 180psi with the throttle closed. So I'm thinking somewhere in the range of 220psi at WOT and that is just too much for the clutch/starter.

I'll keep you guys posted and let you know what kink I need to work out next. Thanks again!!!

 

[N2 H2O]

With the old head, your were probably at 210-230 psi. That's what most of the old race teams used to run. You would have to run race gas and you would definitely need a high torque starter for that much compression.

 

[TreeMoney]

Wanted to update everyone since you provided me with some awesome info.

I finally got this thing running.... Turns out it was the sprag clutch. Compression is right at 180lbs and it runs like a top.

Thanks again guys!

 

[Austin]

Great to hear! sounds like it will be a great running ski!